Variable condenser

ABSTRACT

In a variable condenser, and particularly one of the rotary type, electrical connection between the rotor and an external point such as the ground frame is accomplished in a a contactless manner by means of capacitance defined between the rotor and a fixed part mounted on the frame, that fixed part and the rotor being separated from one another so as to define a gap therebetween. The said connecting capacitance is connected in series with the variable capacitance defined between the rotor and stator and is sufficiently large relative to that variable capacitance so as not appreciably to affect the overall capacitance of the unit. In its preferred form, the capacitance is defined between the rotor shaft and a cylindrical part which surrounds the rotor shaft, and the gap therebetween may be filled with a dielectric material which engages the shaft and serves as a bearing support therefor.

United States Patent [72] Inventor Yasuhiro Takeda Tokyo, Japan [21]App]. No. 66,011 [22] Filed Aug. 21, 1970 [45] Patented Oct. 12, 1971[73] Assignee Alps Electric Co., Ltd.

Tokyo, Japan [32] Priority Sept. 4, 1969 J p 31 1 44/69679 [54] VARIABLECONDENSER 14 Claims, 7 Drawing Figs.

[52] US. Cl 317/254, 334/8 3 [51] Int. Cl H0lg 5/06 [50] Field of Search317/253, 254; 3 34/8 3 [56] References Cited UNITED STATES PATENTS1,742,468 1 1930 Gilling 317/254 Primary Examiner-B A. GoldbergAttorney-James and Franklin ABSTRACT: In a variable condenser, andparticularly one of the rotary type, electrical connection between therotor and an external point such as the ground frame is accomplished ina a contactless manner by means of capacitance defined between the rotorand a fixed part mounted on the frame, that fixed part and the rotorbeing separated from one another so as to define a gap therebetween. Thesaid connecting capacitance is connected in series with the variablecapacitance defined between the rotor and stator and is sufficientlylarge relative to that variable capacitance so as not appreciably toaffect the overall capacitance of the unit. In its preferred form, thecapacitance is defined between the rotor shaft and a cylindrical partwhich surrounds the rotor shaft, and the gap therebetween may be filledwith a dielectric material which engages the shaft and serves as abearing support therefor.

VARIABLE CONDENSER The present invention relates to the structure of avariable condenser, and particularly one of the rotary type, andprovides improved means for making electrical connection to the rotor ofthat condenser.

Condensers of the type under discussion are quite widely employed fortuning purposes in AM, FM and TV receivers. In their most conventionalform, which essentially dates back substantially to the beginning of theradio art, they comprise a stator having a plurality of stator platesand a rotor having a plurality of rotor plates secured to a rotatableshaft. As the shaft is rotated, the rotor and stator plates interleaveand overlap to varying degrees, thereby altering the capacitance betweenthem. In most installations, a plurality of circuits must be tunedtogether (e.g., an antenna circuit, a radiofrequency amplifier circuitand an oscillator circuit), and to that end the rotary variablecondensers employed therewith are generally of ganged constructionhaving a different set of stator and rotor plates for each of thecircuits being tuned. Usually the rotor plates are connected to a commonpotential point, often constituted by the grounded frame or chassis ofthe condenser assembly, the individual stator plates of each set beinginsulatedly mounted on the frame and electrically connected to theirappropriate external circuit in any suitable fashion.

When the rotor plates are all to be connected to a point of commonpotential, it is conventional to utilize a conductive shaft, the rotorplaten not only being mounted thereon but also being electricallyconnected thereto. Means must be provided to electrically connect thatshaft, and therefore the rotor plates of the various ganged sets, to theframe. This means usually comprises resilient conductive connectingelements compressed between the shaft and elements forming a part ofthe'frame. This type of electrical connection is very widely used but issubject to serious disadvantages, particularly with regard to uniformityand reliability of connection. Since either the rotor or frame must moverelative to the connecting element when the condenser is adjusted, wearinescapably occurs and hence the effective life of the assembly isnecessarily limited. Even initially, and much more so as wear occurs,the degree of mechanical engagement between spring connecting elementand rotor will vary as the rotor is turned and thus will cause undesiredvariation in the signal produced. The contact resistance is dependentupon the resiliency of the spring and the cleanliness of the surfaceswhich engage one another; the spring will lose its strength with timeand wear, while rust and corrosion will adversely affect the electricalconnection. The electrical connection is also highly sensitive to anyshock-to which the condenser may be subject.

It is a prime object of the present invention to provide a variablecondenser in which electrical connection is made to the rotor in amanner which eliminates or minimizes the above disadvantages.

It is a further object of the present invention to devise a variablecondenser characterized by long life and simple structure.

It is yet another object of the present invention to provide a variablecondenser in which electrical connection is made to the rotor in acontactless fashion.

It is still a further object of the present invention to provide avariable condenser in which electrical connection is made to the rotorthrough a capacitance defined between the rotor and a part mounted onthe frame and spaced from the rotor so as to define a gap therebetween,the capacitance between the rotor and said part having a magnitude such,in relation to the normal magnitude of the variable capacitance definedbetween the rotor and stator, as not materially to affect the lattermagnitude.

To these ends I provide a variable condenser having a stator with aplurality of stator plates insulatedly mounted on a frame. A rotor shaftis rotatably mounted on that frame, and that shaft carries a pluralityof rotor plates movable with the shaft into varying spatial relation tothe stator plates, thereby to vary the capacitance defined between thoseplates. Electriships between C,, and DC of the circuit ofFlG. 3;

cal connection is made to the rotor plates by means of a capacitor plateor electrode secured to the frame and located in close proximity to therotor, and preferably to the conductive rotor shaft, a gap being definedbetween that plate and the cooperating rotor part, thereby to definetherebetween a capacitance of appropriate magnitude. The said condenserplate or electrode is electrically connected to an external point, andwhen the rotor is to be grounded is electrically connected to thegrounded frame. The gap between the condenser electrode and the rotorshaft may contain a dielectric material which engages both the plate andthe shaft, thereby to provide a supporting or bearing effect on theshaft. To the accomplishment of the above, and to such other objects asmay hereinafter appear, the present invention relates to theconstruction of a variable condenser as defined in the appended claimsand as described in this specification, taken together with theaccompanying drawings, in which:

FIG. 1 is a schematic diagram of a three-gang variable condenser of theprior art;

FIG. 2 is a side elevational view, partially in cross section, of atypical three-gang rotary variable condenser of the prior art such asisschematically shown in FIG. 1;

FIG, 3 is a schematic diagram of the variable condenser of the presentinvention;

FIG. 4 is a graphic representation of the operative relation- FIG. 5 isa schematic diagram of a three-gang variable condenser in accordancewith the present invention;

FIG. 6 is a side elevational view, partially in cross section, of athree-gang variable condenser of the present invention; and

FIG. 7 is a view similar to FIG. 6 but of another embodiment.

Referring to FIGS. I and 2, which respectively disclose schematicallyand physically a conventional arrangement for a three-gang variablecondenser, the three-gang sections being adapted respectively to tune anantenna circuit, a radio frequency amplifier circuit and an oscillatorcircuit, the condenser comprises a U-shaped metallic frame 2 having aninsert 4 of insulating material on which are mounted three sets ofstator plates designated 6, 6' and 6" respectively, each of the sets ofstator plates being insulated from one another and each being adapted tobe connected to their respective tuned circuits in any appropriatemanner. The sets of stator plates are separated by conductive partitions8 electrically connected to the frame 2. A conductive rotor shaft 10 isrotatably mounted in the frame 2 and passes through appropriately shapedopenings formed in the partitions 8. The shaft 10 carries three sets ofrotor plates 12, I2 and 12" which move with the shaft 10 and are adaptedto cooperate with and define a capacitance between themselves and thestator plates 6, 6 and 6", respectively. The degree to which the rotorplates 12 interleave with and overlap the stator plates 6 determines thecapacitance therebetween.

In accordance with the prior art, the rotor plates l2, l2 and 12" areelectrically connected to ground via the condenser frame 2 and thepartitions 8. To accomplish this result in accordance with the priorart, conductive spring clips 14 are employed, those clips beingcompressed between the partitions 8 and shoulders 16 formed in the shaft10 adjacent the points where they pass through the partitions 8.

As has been pointed out, the electrical connection between the rotorplates 12 and ground is, therefore, dependent upon the precise characterof the engagement between the spring clips 14 and the shoulders 16 onthe shaft 10. Any lack of uniformity in that contact engagement as theshaft 10 is rotated will generate electrical noise signals, and isundesirable. As the spring clips 14 lose their resiliency, and as theshoulder surfaces on the shaft 10 become rough, corroded, rusty ordirty, all as is virtually inevitable with the passing of time, thereliability and uniformity of the electrical connection of the rotorplates 12 to ground will be adversely affected. In addition, if thecondenser is subjected to shock, the spring clips 14 will be affectedthereby, again giving rise to the generation of undesirable noisesignals.

FIG, 3 illustrates schematically the principle of the present invention.There C, represents the variable capacitance defined between the statorand rotor plates 6 and 12. C represents the effective capacitance of thecondenser, and C represents a capacitance in series with C, andconnecting the latter to one side of the external circuit, such asground. While C, is a variable capacitance, C, is a fixed capacitance.

In accordance with well-known circuit principles, the overallcapacitance C of the series capacitance circuit of FIG. 3 is given bythe following equation:

c. 1+g c.

As may be seen from the above relationship, if C is sufficiently largerthan C,,, C will be approximately equal to C,,, and as C, varies so willC vary, and to essentially the same degree. Therefore, if it is desiredto connect into the external circuit a capacitance C for tuningpurposes, C may be made equal to C by selecting a value C,, which isonly a little larger than C and selecting C, to have a valuesufficiently larger than C, so that C will be substantially equal toC,,. The cooperative relationship between different values of C and C,for different desired values of C is shown in FIG. 4. From this it willbe seen that if the variable capacitance C,, is connected to ground bymeans of a capacitance C, which is much larger than C, (preferably atleast several times as large) then the stator and rotor plates used toproduce C, need not be appreciably greater than those required in theprior art embodiment of FIGS. 1 and 2, and that the presence of theconnecting capacitance C, makes little change in the resultingcapacitance C if the connecting capacitance C, is sufficiently largerelative to the maximum value of the variable capacitance C,,.

In accordance therewith, in the present invention the rotor plates 12are'connected to'ground (in the embodiment here disclosed to thegrounded frame 2) by means of such a capacitor C the electricalconnection thus being accomplished in a contactless manner. This isschematically indicated in FIG. 5. FIG. 6 is a representation of apreferred structural embodiment of the present invention. It is, in manyrespects, similar to the prior art structure shown in FIG. 2 and, whereappropriate, similar reference numerals are applied to similar parts.The construction of FIG. 6 differs from the construction of FIG. 2substantially solely with respect to the construction utilized where theshaft passes through the partitions 8.

As shown in FIG. 6,the shaft 10 may be uniform in diameter (that aloneconstituting somewhat of a cost saving when compared to the prior artstepped shaft construction of FIG. 2), and the partition 8 carries aconductive part 18 located close to but spaced from the shaft 10, andhere shown as cylindrical in shape through which the conductive shaft 10passes with clearance 20, that clearance constituting an air gap betweenthe shaft 10 and the part 18. Thus the part 18 constitutes a firstcondenser plate and the conductive shaft 10 constitutes a secondcondenser plate, the capacitance therebetween constituting the capacitorC, of FIGS. 3 and 5. The part 18 is mounted on the partition 8 in such amanner as to be electrically as well as physically connected thereto,and hence the rotor plates 12 are connected to ground via the'rotorshaft 10 and the cylindrical part 18, the partition 8 and the frame 2.The magnitude of C, necessary appropriately to cooperate with themaximum magnitude of the variable capacitance C,, provided between thestator and rotor plates 6 and 12 in accordance with the principles setforth above is easily achieved through suitable design of the axiallength of the part 18 and the radial size of the air gap 20.

In the embodiment of FIG. 6 the gap 20 between the cylindrical part 18and the shaft 10 is filled with air. In the alternative embodimentillustrated in FIG. 7 that gap is radially filled over at least aportion of its axial extent with a body 22 of solid or semisoliddielectric material. The dielectric body 22 is supported by thecylindrical part 18 and engages the shaft 10 and therefore supports andprovides a bearin surface for the shaft, rrgrdrfymg the entire structureand ma mg it even more surrounding part 18, or any shocks to which thecondenser may be subjected, will have no appreciable effect on the valueof C, since that value is determined primarily by the magnitude of C,,.Moreover, corrosion or rusting of the opposing surfaces of the shaft 10and the part 18 will have no significant effect on the value of C Hence,the electrical connection of the rotor plates 12 to ground will beeffected reliably and without having to employ precision parts, theconnection will be essentially noiseless from an electrical point ofview, and its life will be relatively unlimited. While a limited numberof embodiments of the present invention have been here specificallydisclosed, it will be apparent that many variations may be made therein,all without departing from the spirit of the invention as defined in thefollowing claims.

I claim:

1. A variable condenser comprising a frame, stator means insulatedlymounted on said frame, rotor means comprising a shaft rotatably mountedon said frame and first plate means on and movable with said shaft andcooperating with said stator means to define a capacitance therebetweenvariable within a given range of magnitudes for different operativepositions of said plate means relative to said stator means, and meansfor making external electrical connection to said rotor means comprisingsecond plate means electrically connected to an external poin't, mountedon said frame so as to be adjacent to but out of engagement with saidrotor means, thereby to define an airgap therebetween, and effective todefine -a capacitance between itself and said rotor means for alloperative positions of said plate means which is sufficiently largerthan the maximum value of said variable capacitance between said rotormeans and stator means so that the magnitude of the total seriescapacitance between said external point and said stator means isessentially that of said variable capacitance.

2. The condenser of claim 1, in which said shaft is conductive, saidfirst plate means is electrically connected thereto, and said secondplate means comprises a conductive part mounted on said frame adjacentand spaced from said shaft.

3. The condenser of claim 2, in which said conductive part iselectrically connected to said frame.

4. The condenser of claim 3, in which dielectric material is located insaid airgap.

5. The condenser of claim 2, in which dielectric material is located insaid airgap.

6. The condenser of claim 2, in which said conductive part at leastpartially surrounds said shaft.

7. The condenser of claim 6, in which dielectric material is located insaid airgap and engages said shaft and said part, thereby to function asa bearing means for said shaft.

8. The condenser of claim 3, in which said conductive part at leastpartially surrounds said shaft.

9. The condenser of claim 8, in which dielectric material is located insaid airgap and engages said shaft and said part, thereby to function asa bearing means for said shaft.

10. The condenser of claim 2, in which said conductive part issubstantially cylindrical and substantially surrounds said shaft.

11. The condenser of claim 10, in which dielectric material is locatedin said airgap and engages said shaft and said part, thereby to functionas a bearing means for said shaft.

12. The condenser of claim 3, in which said conductive part issubstantially cylindrical and substantially surrounds said shaft.

13. The condenser of claim 12, in which dielectric material is locatedin said airgap and engages said shaft and said part, thereby to functionas a bearing means for said shaft.

14. The condenser of claim 1, in which said external point is saidframe.

1. A variable condenser comprising a frame, stator means insulatedlymounted on said frame, rotor means comprising a shaft rotatably mountedon said frame and first plate means on and movable with said shaft andcooperating with said stator means to define a capacitance therebetweenvariable within a given range of magnitudes for different operativepositioNs of said plate means relative to said stator means, and meansfor making external electrical connection to said rotor means comprisingsecond plate means electrically connected to an external point, mountedon said frame so as to be adjacent to but out of engagement with saidrotor means, thereby to define an airgap therebetween, and effective todefine a capacitance between itself and said rotor means for alloperative positions of said plate means which is sufficiently largerthan the maximum value of said variable capacitance between said rotormeans and stator means so that the magnitude of the total seriescapacitance between said external point and said stator means isessentially that of said variable capacitance.
 2. The condenser of claim1, in which said shaft is conductive, said first plate means iselectrically connected thereto, and said second plate means comprises aconductive part mounted on said frame adjacent and spaced from saidshaft.
 3. The condenser of claim 2, in which said conductive part iselectrically connected to said frame.
 4. The condenser of claim 3, inwhich dielectric material is located in said airgap.
 5. The condenser ofclaim 2, in which dielectric material is located in said airgap.
 6. Thecondenser of claim 2, in which said conductive part at least partiallysurrounds said shaft.
 7. The condenser of claim 6, in which dielectricmaterial is located in said airgap and engages said shaft and said part,thereby to function as a bearing means for said shaft.
 8. The condenserof claim 3, in which said conductive part at least partially surroundssaid shaft.
 9. The condenser of claim 8, in which dielectric material islocated in said airgap and engages said shaft and said part, thereby tofunction as a bearing means for said shaft.
 10. The condenser of claim2, in which said conductive part is substantially cylindrical andsubstantially surrounds said shaft.
 11. The condenser of claim 10, inwhich dielectric material is located in said airgap and engages saidshaft and said part, thereby to function as a bearing means for saidshaft.
 12. The condenser of claim 3, in which said conductive part issubstantially cylindrical and substantially surrounds said shaft. 13.The condenser of claim 12, in which dielectric material is located insaid airgap and engages said shaft and said part, thereby to function asa bearing means for said shaft.
 14. The condenser of claim 1, in whichsaid external point is said frame.